1. Field of the Invention
This invention relates generally to methods for constructing dished reflector surfaces and to structures achieved thereby, and more particularly concerns a lightweight, foldable parabolic reflector and a radio frequency antenna assembly incorporating the foldable reflector.
The method and structure of the invention also pertain to the field of solar energy collectors and particularly to foldable lightweight, portable solar energy collectors.
2. State of the Prior Art
Parabolic and spherical reflectors are known and have been used in the field of communications for transmission and reception of radio signals, such as in microwave communication links, space communications and even radio telescopes. Such reflectors have also found application outside the communication areas, as, for example, in the solar energy field where they are used to collect and concentrate solar radiation.
In the past, dished reflectors of significant diameter have been large, heavy and unwieldy assemblies and very inconvenient to transport and install because the curvature of the reflector dish must be held to a high level of accuracy in order to obtain high signal gain and to avoid signal phasing problems at the focal point of the dish.
In the past, these considerations have required rigid reflector structures to achieve precise curvatures except in certain applications where it was found necessary to design parabolic or otherwise curved reflectors of folding construction, such that a reflector may be folded into a compact assembly for transportation and then deployed for use. Notably, such folding reflectors have found application in the space communications field, where space vehicles require relatively large antennas which are folded during launch within the limited space available, and are then deployed outside the earth's atmosphere.
The folding reflector structures of the known prior art have typically included a reflecting mesh supported by a skeleton framework of pivoting radial arms mounted to a central hub. The radial arms were rigid and were manufactured to the desired curvature of the reflector dish. These reflectors are deployed by simply pivoting the radial arms from a generally axial folded position to a generally radial extended or deployed position without any change in the pre-formed curvature of the radial arm. Such precisely curved, pre-formed arms are very expensive to manufacture and become impractical for larger diameter dishes.
The prior art known to the applicant in connection with deployable dish structures is as follows:
Paper No. 100, authored by Lof and Fester, presented at the United Nations Conference on New Sources of Energy, held in Rome in August, 1971.
The Conference proceedings concerning the area of solar energy for heating purposes, originally entitled Volume 5, Solar Energy II, has been republished by Cloudburst Press of America, Inc., 2116 Western Ave., Seattle, Wash. 98121. The title of the republished volume is unknown, but is identified as: ISBN 0-88930-031-3 (soft cover); ISBN 0-88930-032-1 (hard cover).
The reference paper is found at pages 262 through 264 of this volume. The deployable solar cooker disclosed in this paper does not teach the present invention in that it relies only on the curvature of the pre-formed dish of reflecting fabric. As described, the radial spokes are of spring metal and "flex only as forced by the fabric."
Man's Greatest Adventure by Laurence Allen, 1974, Library of Congress Card No. 74-17235, includes various photographs showing deployable antennas used on the lunar space mission. In particular, a small portable folded S-band dish antenna is shown at page 46. The S-band antenna photographs do not teach a curved dish structure in cooperative relationship with an independently stressed spoke framework.
The tripod-mounted S-band antenna is considerably smaller than the dishes contemplated by the applicant's invention. The structure shown in the reference, if enlarged and deployed in a 1 G gravitational field, would not be sufficiently rigid to define a usable self-supporting dished reflector surface. The small deployable dish mounted on the lunar rover vehicle has rigidly curved radial support arms.
The ARRL Antenna Handbook, published by the American Relay League, shows at pages 254 and 255 a 12-foot stressed parabolic dish antenna. This structure is not deployable and spokes are stressed by guy wires attached to the focus feed support boom which is not self-supporting. The perimeter wire of the reference serves as a peripheral support means for attaching the wire mesh of the reflector to the rib skeleton.
It is contemplated in the reference that the dish be made portable by removing the mesh sheet, and disassembling the rib structure. Upon reassembly, the mesh is attached by folding the edges over the wire perimeter. The ribs lie over the frontal reflecting surface of the mesh sheet, whereas in applicant's antenna the reflector surface is unbroken and the radial spokes are attached to the rear of the pliable reflector dish.
The applicant is not aware of folding dish reflectors in the 9- to 16-foot diameter range for use on the earth's surface, that is, in a 1 G gravitational field.